Copper alloy, copper alloy producing method, copper complex material, and copper complex material producing method

ABSTRACT

An element such as Cr is caused to dissolve sufficiently in a base-material metal (Cu) in a solid solution state at a high temperature and a material in a supersaturated condition is obtained by performing quenching. After that, a strain is applied to this material and this material is subjected to aging treatment at a low temperature simultaneously with or after the application of this strain. As a result of this, it is possible to obtain a copper alloy having properties desirable as an electrode material, for example, a hardness of not less than 30 HRB, an electrical conductivity of not less than 85 IACS %, and a thermal conductivity of not less than 350 W/(m·K).

TECHNICAL FIELD

The present invention relates to a copper alloy and a composite coppermaterial that are suitable for wiring connectors of electric vehicles orthe like and electrode materials for welding, and methods ofmanufacturing the copper alloy and the composite copper material.

BACKGROUND ART

With the increasing EV (electric vehicle) design of automobiles, theconsumption of harnesses and connectors that are connection parts ofwires tends to increase. In the adoption of EVs, ensuring safety and gasmileage by electronic control techniques is also a purpose.

Connectors that are incorporated in automobiles are used in severeenvironments of high temperature and vibration and, therefore, thereliability of connection and contact stability are required. Also, withincreasing adoption of EVs, copper-based materials that have smallenergy losses, i.e., high conductivity are desired.

Also for electrode materials for welding, properties having values aboveprescribed ones are required in all respects of mechanical strength,thermal properties and electrical properties.

For mechanical strength, it is known as the Hall-Petch law thatmechanical strength is generally improved by refining the crystalstructures of metal materials.

For example, when metal or alloy materials are deformed, materialstrength increases due to work hardening. This is understood as follows.That is, various kinds of defects (point defect, dislocation, stackingfault, etc.) are accumulated in materials due to working (plasticdeformation), and as a result of the interactions of these defects, theintroduction and migration of new defects become difficult and thematerials obtain resistance to external force.

To apply plastic deformation (strain) to metal materials, extrusion,drawing, shearing, rolling, forging, etc. have hitherto been carriedout. Concretely, the HIP (High Pressure Torsion) process that involvestwisting a material while applying high pressure to the material, theCEC (Cyclic Extrusion Compression) process that involves repeatedlythreading a material through a constricted pipe, and the ARB(Accumulative Roll Bonding) process that involves cutting a metal sheetthe thickness of which has been reduced by rolling and repeatedlyrolling superimposed metal sheets have been proposed, and in particular,as a concrete method of refining the grains of an aluminum alloy, theECAE (equal-channel-angular extrusion) process that involves applyingshearing deformation to a material by lateral extrusion without areduction of sectional area of the material has been proposed asdisclosed in the Japanese Patent Laid-Open No. 9-137244, the JapanesePatent Laid-Open No. 10-258334, the Japanese Patent Laid-Open No.11-114618, the Japanese Patent Laid-Open No. 2000-271621, etc.

On the other hand, for copper alloys, methods disclosed in the JapanesePatent Laid-Open No. 11-140568, the Japanese Patent Laid-Open No.2000-355746, etc. have been proposed. In these conventional techniques,to improve the properties (machinability and dezincification corrosion)of brass (Cu—Zn) that is used as a material for water faucet fittingsand the like among other copper alloys, dynamic recrystallization iscaused to occur by hot extrusion thereby to obtain the refinement ofcrystal grains and specific ratios of crystal structures (ratios of theα-phase, β-phase and γ-phase).

Also, to bring out prescribed properties from age-hardening type copperalloys to which an element that does not dissolve or scarcely dissolvesin a solid solution state at room temperature, such as chromium (Cr),zirconium (Zr), beryllium (Be), titanium (Ti) and boron (B), is added,this element is first caused to dissolve sufficiently in a solidsolution sate at a high temperature and then quenched and brought to asupersaturated condition, which is followed by aging treatment at aprescribed temperature, thereby causing the added element in asupersaturated condition to precipitate.

Even when the above-described work aging or aging treatment for aluminumalloys and copper alloys is applied as it is to age-hardening typecopper alloys to which an element, such as chromium (Cr), zirconium(Zr), beryllium (Be), titanium (Ti) and boron (B), is added, it isimpossible to simultaneously satisfy all respects of mechanicalstrength, thermal properties and electrical properties.

That is, in order to ensure that the thermal properties and electricalproperties required of connectors used in electric vehicles or the like,electrode materials, etc. are developed, it is necessary to ensure thatan added element that dissolves in a solid solution state is caused toprecipitate in the largest possible amount. In order to cause thiselement to precipitate in a large amount, it is necessary to raise theaging temperature. However, when the aging temperature is raised, graingrowth proceeds and mechanical properties decrease. That is, mechanicalstrength and thermal and electrical properties are in a tradeoffrelation.

For thermal properties and electrical properties, copper alloys in whichan oxide such as alumina is dispersed in the copper matrix are excellentin electrical conductivity and heat resistance and, therefore, thesecopper alloys are widely used in materials for electric parts. Manyproposals to improve the properties and manufacturing methods of thesecopper alloys have been made.

For example, a proposal has been made to improve electrical conductivityand softening properties by adding, as elements that perform internaloxidation, not only aluminum, but also tin as a third element. (JapanesePatent Laid-Open No. 59-150043)

There has been proposed a copper alloy in which the amount of particlesof not more than 50 μm is not less than 70 wt % owing to the use of acopper alloy powder of not more than 300 μm which is manufactured by theatomizing process and in which a readily oxidizing metal such asaluminum is caused to dissolve in a solid solution state. (JapanesePatent Laid-Open No. 60-141802)

There has also been proposed a method that involves internally oxidizinga Cu—Al alloy powder thereby to convert Al to Al₂O₃, making the surfaceof this alloy powder smooth, green compacting the powder to form a greencompact, and hot forging this green compact at 600 to 1,000° C.(Japanese Patent Laid-Open No. 63-241126)

Also, there has been proposed a method that involves internallyoxidizing a plate-like copper alloy containing Al to convert Al toAl₂O₃, working this plate-like alloy in coil form, sealing this coiledalloy in a metal tube, and hot working this metal tube at 900° C. in adesired shape. (Japanese Patent Laid-Open No. 2-38541)

Also, there has been proposed a method that involves filling an alloypowder obtained by internally oxidizing Cu—Al alloy chips in a carbondie and hot pressing the alloy powder at 900° C. and at a pressure of400 kg/cm². (Japanese Patent Laid-Open No. 2-93029)

Furthermore, there has been proposed a method that involves improvingsinterability by causing an annular hard layer of Al₂O₃ to be present inthe interior of a Cu—Al alloy powder. (Japanese Patent Laid-Open No.4-80301)

In all of the above-described conventional techniques, hot working athigh temperatures is performed and, therefore, structures tend to becomecoarse due to grain growth. Thus, in the conventional methods, it isimpossible to obtain materials that simultaneously satisfy, as theproperties required of connectors of electric vehicles and electrodematerials for welding, the requirements that hardness be not less than30 HRB, preferably not less than 40 HRB, that electrical conductivity benot less than 85 IACS %, preferably not less than 90 IACS %, and thatthermal conductivity be not less than 350 W/(m·K), preferably not lessthan 360 W/(m·K).

When hardness is not less than 30 HRB, it is possible to prevent the tipof an electrode material from becoming deformed and generating heat.When electrical conductivity is not less than 85 IACS %, it is possibleto prevent an electrode material from reacting with a steel sheet andsticking to the steel sheet. When thermal conductivity is not less than350 W/(m·K), it is possible to prevent the deposition of an electrodematerial during welding because the cooling efficiency increases.

Because Al₂O₃ does not dissolve in Cu in a solid solution state even ata high temperature, a conventional technique by which Al₂O₃ is caused toprecipitate by aging treatment after dissolution in a solid solutioncannot be applied to a Cu—Al alloy.

DISCLOSURE OF THE INVENTION

A material that simultaneously satisfies all of the mechanical strength,thermal properties and electrical properties required of a material forconnectors used in the wiring of electric vehicles or an electrodematerial for welding is obtained by ensuring that a second element thatdissolves in a solid solution state at a high temperature, but does notdissolve or scarcely dissolves in a solid solution state (cannotmaintain a solid solution state) at room temperature is caused todissolve in a base-material metal (Cu) in a solid solution state, thatcrystal grain refinement is achieved by applying a strain equivalent toan elongation of not less than 200% to this material, and that thismaterial is subjected to aging treatment simultaneously with or afterthe application of this strain, thereby to promote precipitation of thesecond element among crystal grains.

Concretely, in a copper alloy containing a second element that does notdissolve or scarcely dissolves in a solid solution state at roomtemperature, it is possible to obtain a copper alloy the average grainsize of which is not more than 20 μm and in which the second elementprecipitates among crystal grains. This copper alloy has a hardness ofnot less than 30 HRB, an electrical conductivity of not less than 85IACS %, and a thermal conductivity of not less than 350 W/(m·K). Thesecond element is any of chromium (Cr), zirconium (Zr), beryllium (Be),titanium (Ti) and boron (B).

Extrusion, drawing, shearing, rolling or forging can be considered asmeans for applying a strain to the material and conditions for theextrusion are such that lateral extrusion is performed at a dietemperature of 400 to 500° C. and an extrusion speed of 0.5 to 2.0mm/sec. It is also possible that before a strain is applied to thematerial, the material is subjected to aging treatment beforehand.

On the other hand, in order to obtain a material that simultaneouslysatisfies all of the mechanical strength, thermal properties andelectrical properties from a ceramic powder (alumina or titanium boride)that does not dissolve in copper in a solid solution state even at ahigh temperature, a copper powder and a ceramic powder are mixedtogether, thereby to form a mixed powder as a primary shaped body, and astrain is applied to this primary shaped body, thereby to form asecondary shaped body in which base material and ceramic particles arecombined together with refined particle sizes. As a result of this, acomposite copper material having a hardness of not less than 60 HRB, anelectrical conductivity of not less than 85 IACS %, a thermalconductivity of not less than 350 W/(m·K), and a hardness of not lessthan 30 HRB is obtained.

Incidentally, as the means for applying a strain, for example, lateralextrusion is performed at a material temperature of not less than 400°C. but not more than 1,000° C. and a die temperature of not less than400° C. but not more than 500° C. Why the specified raw materialtemperature is 400° C. to 1,000° C. is that if the raw materialtemperature is less than 400° C., extrusion becomes difficult because oflarge deformation resistance and sufficient bonding strength cannot beobtained between the parent phase (matrix) and particles and that if theraw material temperature exceeds 1,000° C., this temperature exceeds themelting point of copper and copper melts, making it impossible to applya strain. The reason why the specified die temperature is 400° C. to500° C. is that if the die temperature is too low, extrusion becomesdifficult and if die temperature is too high, the die itself becomesannealed.

The primary shaped body can be obtained by green compacting or byfilling the mixed powder in a tube. Furthermore, the average particlesize of the ceramic powder is 0.3 to 10 μm, a strain applied to theprimary shaped body is equivalent to an elongation of not less than200%, the average particle size of a base material of the secondaryshaped body to be obtained is not more than 20 μm, and the averageparticle size of ceramic particles is not more than 500 nm.

As described above, because titanium boride is not mixed with a copperpower and instead, a titanium powder that becomes titanium boride as aresult of a reaction and a boron powder are formed in the copper matrix,it is possible to increase mechanical strength as fine particles.Therefore, in another aspect of the invention, a method of manufacturinga composite copper material in which titanium boride is dispersed in thecopper matrix comprises the following steps [1] to [3]:

[1] the step of mixing a copper powder, a titanium powder and a boronpowder together, thereby to form a primary shaped body;

[2] the step of giving thermal energy to the primary shaped body,thereby causing the titanium powder and the boron powder to react witheach other in order to form titanium boride in a copper matrix; and

[3] the step of applying a strain to the primary shaped body in whichthe titanium boride is formed by plastically deforming the primaryshaped body, thereby to form a secondary shaped body.

For example, if the average grain size of a titanium powder and a boronpowder is 0.3 to 10 μm, it can be ensured that the average particle sizeof a base material of the secondary shaped body to be obtained is notmore than 20 μm, and that the average particle size of titanium borideparticles is not more than 400 nm, and hence it is possible to obtain acomposite copper material having small deformation by pressurizationduring welding as an electrode material for welding (due to lowcompressive strength of the material).

Part of titanium and boron dissolve in copper in a solid solution statewhen thermal energy is applied to the primary shaped body. However, ifthe titanium and boron in this solid solution state remain in anunreacted condition, the composite copper material is inferior inelectrical conductivity and thermal conductivity. Therefore, it ispreferred that the secondary shaped body be subjected to heat treatmentin the same step as the step of applying a strain by plastic deformationor a step following this step, whereby the unreacted solute elements(titanium and boron) are caused to precipitate.

The means for applying plastic deformation, the material temperature,the die temperature, the extrusion speed and the number of times ofextrusion are the same as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing to explain the steps for obtaining a copper alloyrelated to the invention;

FIG. 2 is a drawing to explain a die used in the ECAE treatment;

FIG. 3( a) is a micrograph of a crystal structure of a copper alloyrelated to the invention;

FIG. 3( b) is a micrograph of a crystal structure before ECAE treatment;

FIG. 4 is a graph that shows the relationship between die temperatureand hardness;

FIG. 5 is a graph that shows the relationship between die temperatureand electrical conductivity;

FIG. 6 is a graph that shows the relationship between die temperatureand thermal conductivity;

FIG. 7 is a graph that compares the weldability of a copper alloyobtained by a manufacturing method related to the invention with that ofconventional copper alloys in terms of the occurrence of spatters andweld sticking;

FIG. 8 is a graph that compares the weldability of a copper alloyobtained by a manufacturing method related to the invention with that ofconventional copper alloys in terms of the number of welds in continuousspot welding;

FIG. 9 is a graph that shows the relationship between the amount ofadded Ti and electrical conductivity of a copper alloy subjected toaging treatment and a copper alloy not subjected to aging treatment;

FIG. 10 is a graph that shows the relationship between the amount ofadded Ti and electrical conductivity of a copper alloy subjected toaging treatment and a copper alloy subjected to aging treatment andheavy working (applying a strain equivalent to an elongation of not lessthan 200%);

FIG. 11 is a graph that shows the relationship between the amount ofadded Ti and hardness (mHV) of a copper alloy subjected to agingtreatment and a copper alloy subjected to aging treatment and heavyworking (applying a strain equivalent to an elongation of not less than200%);

FIG. 12 is a graph that shows the relationship between electricalconductivity and hardness (mHV);

FIG. 13 is a graph that shows the relationship between methods of addingTiB and electrical conductivity;

FIG. 14 is a drawing to explain a method of manufacturing a compositecopper material related to the invention;

FIGS. 15( a) and 15(b) are each a micrograph of a crystal structure of acopper alloy obtained by a manufacturing method related to theinvention, FIG. 15( a) showing a composite copper alloy to which aluminais added and FIG. 15( b) showing a composite copper alloy to whichtitanium boride is added;

FIG. 16 is a graph that compares the weldability of composite coppermaterials obtained by a manufacturing method related to the inventionwith that of a conventional composite copper material in terms of thenumber of welds in continuous spot welding;

FIG. 17 is a drawing to explain a method of manufacturing a compositecopper material related to the invention;

FIG. 18 is a micrograph that shows the condition of a structure aftersintering; and

FIG. 19 is a drawing that shows the relationship between electricalconductivity and amount of added TiB when heavy working is performed andwhen heavy working is not performed.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIG. 1, first Cr is caused to melt into a base material (Cu)in an amount of 0.1 to 1.4 wt % and a material in which Cr dissolves inCr in a solid solution state in a supersaturated manner is obtained byquenching the melt. Subsequently, a strain equivalent to an elongationof not less than 200% is applied to this material. Incidentally, it isdesirable to use a material that is subjected to aging treatment aftersolution treatment.

When an added element is Zr, the Zn content is 0.15 to 0.5 wt %. In thecase of Be, the Be content is 0.1 to 3.0 wt %. In the case of Ti, the Ticontent is 0.1 to 6.0 wt %. And in the case of B, the B content is 0.01to 0.5 wt %.

FIG. 2 shows a die that applies a strain by use of a Cu tube. Theabove-described mixture is filled in the Cu tube and extruded at a dietemperature of 400 to 500° C. and an extruding speed of about 1 mm/secby repeating the extrusion four times (ECAE treatment). Thus, a strainis applied to a copper alloy in which Cr dissolves in a solid solutionstate in a supersaturated manner. By this operation, the crystal grainsize decreases to not more than 20 μm from 200 μm.

If Δe: amount of strain, ψ:½ of inner angle of joint, ERR: area ratiobefore and after working, A0: sectional area before working, A:sectional area after working, EAR: reduction ratio of equivalentsectional area before and after working, EE: equivalent strain(elongation), then the following relationships hold:Δe=2/√3 cotan ψERR=A0/A=exp(Δe)EAR=(1−1/ERR)×100EE=(ERR−1)×100

The crystal structure becomes grain-refined by the above-describedlateral extrusion (ECAE treatment). Because extrusion conditions overlapaging treatment, the precipitation of a second element is promoted atthe same time with grain refinement.

The crystal structure of a copper alloy obtained by this ECAE treatmentis shown in a micrograph of FIG. 3( a). The crystal structure beforeECAE treatment is shown in a micrograph of FIG. 3( b). From thesemicrographs, it is apparent that an added element has precipitated(black points in the photograph) among crystal grains due to the ECAEtreatment.

FIG. 4 is a graph that shows the relationship between die temperatureand hardness, FIG. 5 is a graph that shows the relationship between dietemperature and electrical conductivity, and FIG. 6 is a graph thatshows the relationship between die temperature and thermal conductivity.From these graphs it is apparent that a copper alloy related to theinvention has properties required of an electrode material such as awelding tip, i.e., a hardness of not less than 30 HRB, an electricalconductivity of not less than 85 IACS %, and a thermal conductivity ofnot less than 350 W/(m·K).

That is, from FIGS. 4 to 6, it is apparent that a material not subjectedto ECAE treatment (solution treatment+aging treatment) is inferior inelectrical conductivity and thermal conductivity although it has highhardness, that a material obtained by subjecting a material which hasbeen subjected to only the solution treatment to ECAE treatment isexcellent in electrical conductivity and thermal conductivity althoughit has low hardness, and that a material obtained by subjecting amaterial which has been subjected to aging treatment after solutiontreatment to ECAE treatment is excellent in all respects of hardness,electrical conductivity and thermal conductivity.

FIG. 7 is a graph that compares the weldability of a copper alloyobtained by a manufacturing method related to the invention with that ofconventional copper alloys in terms of the occurrence of spatters andweld sticking. The copper alloy related to the invention is equivalentto the alumina-dispersed copper and the copper alloy before agingtreatment in terms of appropriate current conditions, and weld stickingdoes not occur.

FIG. 8 is a graph that compares the weldability of a copper alloyobtained by a manufacturing method related to the invention with that ofconventional copper alloys in terms of the number of welds in continuousspot welding. When the copper alloy related to the invention was used asa welding tip, it was possible to produce 1475 welds in continuous spotwelding.

As described above, a copper alloy related to the invention has a finecrystal structure and a large amount of added element precipitates amongcrystal grains and, therefore, it is possible to ensure that a copperalloy related to the invention simultaneously provides mechanicalstrength and thermal and electrical properties that have hitherto beenin a tradeoff relation.

In particular, it is possible to obtain a copper alloy that has theproperties required of an electrode material such as a welding tip,concretely, a hardness of not less than 30 HRB, an electricalconductivity of not less than 85 IACS %, and a thermal conductivity ofnot less than 350 W/(m·K).

Next, titanium (Ti) was selected as an element to be added and copperalloys were obtained in the same method as described above. Results areshown in FIGS. 9 to 12.

FIG. 9 is a graph that shows the relationship between the amount ofadded Ti and electrical conductivity. The maximum degree of dissolutionof Ti in a solid solution state is essentially about 8 wt % and is notvery large. As shown in FIG. 9, even after aging treatment, about 0.5 wt% of Ti remains in a solid solution state. It might be thought that thisTi in a solid solution state lowers the electrical conductivity ofcopper alloys.

FIG. 10 is a graph that shows the electrical conductivity of a copperalloy that is heavily worked (by application of a strain equivalent toan elongation of 200%) after being subjected to aging treatment at 470°C. for two hours and the electrical conductivity of a copper alloysubjected to only aging treatment. From this graph it is apparent thatthe electrical conductivity of the heavily worked copper alloy increasesgreatly. It might be thought that this is because the Ti in a solidsolution state precipitates due to heavy working.

FIG. 11 is a graph that compares the hardness of a heavily worked copperalloy with that of a copper alloy subjected to only aging treatment. Asshown in this graph, the hardness of the heavily worked copper alloy islower than that of the copper alloy subjected to only aging treatment.It might be thought that the Ti that has contributed to solid solutionstrengthening precipitates due to heavy working.

FIG. 12 is a graph that shows the relationship among hardness,electrical conductivity and heavy working temperature. From this graphit is apparent that a Cu—Ti alloy is inferior in electrical conductivityand that electrical conductivity increases although hardness decreaseswith increasing heavy working temperature. Also in this case, it mightbe thought that the Ti that has contributed to solid solutionstrengthening precipitates due to heavy working.

Thus, by combining heavy working with aging treatment, it becomespossible to cause the Ti that dissolves in a solid solution state toprecipitate from the copper matrix although it has hitherto beenimpossible to cause this Ti to precipitate by aging treatment. Inaddition, the amount of Ti that precipitates can be controlled bycontrolling the degree of heavy working. Therefore, it is possible tomake a copper alloy having properties that suit the purpose.

Next, boron (B) was selected as an element to be added, and copperalloys were made by various methods. The relationship between the boron(TiB) of the obtained copper alloys and electrical conductivity is shownin FIG. 13. As methods of obtaining the copper alloys, [1] preparationof a refined material subjected to solution treatment, [2] addition of aTiB₂ powder as a compound (ceramic) to copper, and [3] a method ofadding a Ti powder and a B powder independently to copper were adopted.

From FIG. 13, it became apparent that in all cases electricalconductivity decreases with increasing addition ratio of TiB and that interms of manufacturing methods, the highest electrical conductivity isobtained in the case of a refined material although electricalconductivity increases by performing heavy working.

FIGS. 14 to 16 explain another embodiment (a composite copper material).First, as shown in FIG. 14, an alumina (Al₂O₃) powder or a titaniumboride (TiB₂) is mixed with a base material (a Cu powder). The mixingproportion is 0.1 wt % to 5.0 wt %. If the mixing proportion is lessthan 0.1 wt %, wear resistance is not improved. If the mixing proportionexceeds 5.0 wt %, electrical conductivity decreases and die life alsoshortens. Therefore, the above-described range is specified.

Subsequently, the above-described mixed powder is formed into a primaryshaped body in order to perform lateral extrusion. A primary shaped bodyis formed, for example, by green compacting or by filling the mixedpowder in a Cu (copper) tube. Subsequently, a strain equivalent to notless than 200%, preferably, about 220% is applied to the primary shapedbody by lateral extrusion.

Incidentally, in FIG. 14, for the sake of easy understanding, thediameter of the Cu tube is larger than the diameter of an insertion holeformed in the die. In actuality, however, the diameter of the Cu tube isalmost the same as the diameter of the insertion hole formed in the die.The Cu tube is supported with a jig or the like so that the Cu tube doesnot fall while the Cu tube is being pushed in by use of a punch.

Concrete conditions for the lateral extrusion are such that the dietemperature is 400 to 1000° C. and the extrusion speed is about 1mm/sec, and ECAE treatment is performed by repeating extrusion 12 timesunder the conditions. By repeating the extrusion, the parent phasebecomes grain-refined and the crushing and dispersion of the ceramicoccur.

The micrographs of crystal structures of the copper alloys obtained bythis ECAE treatment are shown in FIGS. 15( a) and 15(b). FIG. 15( a)shows a composite material to which an alumina powder is added, and FIG.15( b) shows a composite material to which a titanium boride powder isadded. From these photographs, it is ascertained that alumina ortitanium boride having a particle size of several nanometers isuniformly dispersed in the copper matrix.

FIG. 16 is a graph that compares the weldability of composite coppermaterials obtained by a manufacturing method related to the inventionwith that of a conventional composite copper material in terms of thenumber of welds in continuous spot welding. The number of welds incontinuous spot welding is about 1200 when a commercially availablecomposite copper material in which alumina is dispersed in copper isused as a welding tip, whereas the number of welds in continuous spotwelding is about 1600 in the case of an alumina-dispersed compositecopper material subjected to ECAE (equal-channel-angular-extrusion)treatment and 1900 welds in continuous spot welding were possible when acomposite copper material related to the invention in which titaniumboride is dispersed was used as a welding tip.

Because solution treatment is not a starting point in this embodiment,there is no restriction by the limit of dissolution in a solid solutionstate and it is possible to arbitrarily set the proportion of theparticles of a second element (Al₂O₃ or TiB₂) in a copper alloy.Therefore, it is possible to obtain properties that could not beobtained in conventional composite copper materials.

That is, the purity of the matrix of a copper alloy is high, a copperalloy is excellent in electrical properties, and the particle size ofparticles of Al₂O₃ or TiB₂ that precipitate at the interfaces of matrixparticles is on the order of nanometers (not more than 500 nm) becauseof the suppression of grain growth. Also, the amount to be added can bearbitrarily set.

Next, a description will be given of an embodiment in which as astarting material, a titanium (Ti) powder and a boron (B) powder aremixed with the base material (Cu powder).

FIG. 17 is a drawing to explain the processes for obtaining a compositecopper material related to the embodiment, in both of which the mixingproportion of both the titanium powder and the boron powder in thestarting material is 0.1 wt % to 5.0 wt %. If the mixing proportion isless than 0.1 wt %, wear resistance is not improved. If the mixingproportion exceeds 5.0 wt %, electrical conductivity decreases and dielife also shortens. Therefore, the above-described range is specified.

Subsequently, the above-described mixed powder is formed into a primaryshaped body in order to perform lateral extrusion. There are availabletwo processes for obtaining a primary shaped body. When a product to beproduced is a small one like a connector and an electrode rod, theabove-described mixture is filled in the Cu tube to form a primaryshaped body. On the other hand, when a product to be produced is a longone or a large-sized one, a primary shaped body is formed by greencompacting.

Subsequently, the above-described primary shaped body is sintered. Theadded titanium (Ti) and boron (B) react due to the thermal energyresulting from this sintering to form titanium boride. FIG. 18 shows thecondition of a structure after sintering. From this figure it isapparent that the titanium boride not formed before sintering is formedin the copper matrix after sintering.

Incidentally, although sintering was performed as means for applyingthermal energy in the embodiment, thermal energy may be applied by meansother than this.

A strain equivalent to not less than 200%, preferably not less thanabout 220% is applied to the primary shaped body after sintering thusobtained by lateral extrusion. The lateral extrusion is performed by thesame method as described above.

Concrete conditions for the lateral extrusion are such that the materialtemperature is 400 to 1000° C., the die temperature is 400 to 500° C.and the extrusion speed is about 1 mm/sec, and ECAE(equal-channel-angular-extrusion) treatment is performed by repeatingextrusion 12 times under the conditions. By repeating the operation, theparent phase becomes grain-refined and the crushing and dispersion ofthe titanium boride formed in the copper matrix occur.

FIG. 19 is a drawing that shows the relationship between electricalconductivity and amount of added TiB when heavy working (applying astrain equivalent to an elongation of 220%) is performed and when heavyworking is not performed. From this figure it became apparent thatelectrical conductivity is increased by heavy working. Although titaniumboride having electrical conductivity is formed by the above-describedheat treatment, electrical conductivity cannot be increased. It is notthat the added titanium and boron react stoichiometrically, but that theadded titanium and boron in a solid solution state remain within thecopper matrix while they are still unreacted. Therefore, it might bethought that the unreacted solute elements (titanium and boron)precipitate when heavy working is performed, with the result thatelectrical conductivity increases.

Also for complex copper materials related to the invention, weldabilitywas verified by the number of welds in continuous spot welding and thesame results as shown in FIG. 16 were obtained.

Because solution treatment is not a starting point in a method ofmanufacturing a composite copper material related to this embodiment,there is no restriction by the limit of dissolution in a solid solutionstate, and it is possible to arbitrarily set titanium and boron to beadded to copper, and it is possible to obtain properties that could notbe obtained in conventional composite copper materials.

In particular, because titanium boride is not directly added to copperand because titanium and boron before the reaction are added to causetitanium boride to be formed in the copper matrix by the reaction byapplying thermal energy to the titanium and boron before the reaction,the grain refinement of a structure (in the order of nanometers: notmore than hundreds of nanometers) is promoted and mechanical strengthincreases.

INDUSTRIAL APPLICABILITY

A copper alloy and a composite copper material related to the inventioncan be used as a material for a connector that constitutes part ofwiring of electric vehicles and the like or a material for weldingelectrodes.

1. A method for manufacturing a copper alloy welding electrode tip of awelding machine, comprising the steps of: enabling any of chromium (Cr),zirconium (Zr), beryllium (Be), titanium (Ti) and boron (B) to dissolvein a solid solution in a base-material metal (Cu) as a second elementthat does not dissolve or scarcely dissolves in copper in a solidsolution state at room temperature, wherein respective addition ratiosof the second element being Cr:0.1 to 1.4 wt %, Zr:0.15 to 0.5 wt %,Be:0.1 to 3.0 wt %, Ti:0.1 to 6.0 wt %, B:0.01 to 0.5 wt %, applying astrain equivalent to an elongation of not less than 200% to thismaterial to achieve crystal grain refinement, wherein strain is appliedby extruding the material, and extrusion conditions are such thatlateral extrusion is performed at a material temperature of 400 to1,000° C., a die temperature of 400 to 500° C., and an extrusion speedof 0.5 to 2.0 mm/sec, and subjecting this material to aging treatmentsimultaneously with or subsequent to application of this strain, therebypromoting precipitation of the second element among crystal grains.
 2. Amethod for manufacturing a copper alloy welding electrode tip of awelding machine comprising the steps of: enabling any of chromium (Cr),zirconium (Zr), beryllium (Be), titanium (Ti) and boron (B) to dissolvein a solid solution in a base-material metal (Cu) as a second elementthat does not dissolve or scarcely dissolves in copper in a solidsolution state at room temperature, wherein respective addition ratiosof the second element being Cr:0.1 to 1.4 wt %, Zr:0.15 to 0.5 wt %,Be:0.1 to 3.0 wt %, Ti:0.1 to 6.0 wt %, B:0.01 to 0.5 wt %, applying astrain equivalent to an elongation of not less than 200% to thismaterial to achieve crystal grain refinement, wherein strain is appliedby extruding the material, and extrusion conditions are such thatlateral extrusion is performed at a material temperature of 400 to 1000°C. a die temperature of 400 to 500° C., and an extrusion speed of 0.5 to2.0 mm/sec, and subjecting this material to aging treatment before thisstrain is applied to the material.